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Variation in Pinniped Dentition

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Variation in Pinniped Dentition VARIATION IN PINNIPED DENTITION by CAITLYN BOATMAN A THESIS Presented to the Department of Biology and the Robert D. Clark Honors College in partial fulfillment of the requirements for the degree of Bachelor of Science September 2018 An Abstract of the Thesis of Caitlyn Boatman for the degree of Bachelor of Arts in the Department of Biology to be taken September 2018 Title: Variation in Pinniped Dentition Approved: _______________________________________ Samantha Hopkins I studied variation in the teeth of 5 different species of pinniped: E. jubatus, Z. californianus, P. vitulina, E. barbatus, and O. rosmarus. Prior to this study, little work had been done on dental variation in marine mammals with homodont teeth. Most studies have looked specifically at terrestrial carnivores such as C. lupus and F. silvestris. Specifically, I compared the coefficient of variation of a few different aspects of dentition (total surface area, individual tooth surface area, toothrow length, tooth width and blade length) and compared them to CVs of other published terrestrial mammals. In general, I determined that pinniped dentition was much more variable than dentition of terrestrial species (i.e. had higher CVs). In addition, I determined that blade length, toothrow length, and total surface area is correlated with body size. Larger bodied animals or species have larger surface areas, toothrow lengths, and blade lengths. Even when normalized for body size, variation in mean sizes of each of these aspects persisted, suggesting there is no ideal toothrow length, blade length, or total tooth surface area needed for survival. ii Acknowledgements I would like to thank Professor(s) Samantha Hopkins, Edward Davis, Win McLaughlin and other names thereafter, for helping me to fully examine the specific topic and consider the various perspectives and contexts related to this subject matter. Thank you for all your assistance and guidance throughout the entire project. Thank you to all members of Hopkins lab for extra guidance and assistance. Thank you to Win McLaughlin for assisting in photography specimens. Thank you to the museums FMNH, UWBM, UAM, MNCH, and MVZ for providing specimens. Thank you Chris J. Conroy for allowing me to visit the Museum of Vertebrate Zoology in person and photograph specimens at that location. Thank you to my family, Abby Graham, and Riley Cole for support throughout my college experience. iii Table of Contents Introduction 1 Methods 9 Specimen Collection 9 Camera Views 12 Statistics 14 Results 17 Coefficients of Variation 17 Relationship to Palate Length 22 Relationships In Mean Sizes Between Species 26 Discussion 31 Future Directions 37 Bibliography 38 Supplementary Information 42 iv List of Figures Figure 1: Camera Views. 11 Figure 2: Measurements. 13 Figure 3: Plots of coefficients of variation and specific aspect for right surface areas, right tooth widths, blade length, and left and right tooth length. 20 Figure 4: Plots of coefficients of variation for right surface areas, right tooth widths, blade length, and left and right tooth length. 21 Figure 5: Relationship of palate length to right toothrow length. 23 Figure 6: Relationship of palate length to left toothrow length. 24 Figure 7: Relationship of logged palate length to logged blade length and logged total surface area. 25 Figure 8: Comparison of right and left toothrows for each species. 26 Figure 9: Comparison of total surface area and blade length for each species. 27 Figure 10: Comparison of mean right toothrow length, blade length, and total surface area when each of those aspects is divided by palate size. 29 S1: Q-Q plots for OLS that are not normally distributed. 42 S2: Q-Q plots for ANOVAs that are not normally distributed (un-normalized). 43 S3: Q-Q plots for ANOVAs that are not normally distributed (normalized). 44 v List of Tables Table 1: Table displaying coefficients of variation for canine and tooth surface area in each species. 17 Table 2: Table displaying coefficients of variation for each species for tooth-row length, blade length, and right tooth width. 18 Table 3: Table displaying average coefficients of variation for each aspect. 18 Table 4: Table with some sample characteristics of different species and their corresponding CVs. 31 vi Introduction Warm blooded mammals, because they require a great deal of energy to continually heat their bodies, demand an efficient way to process their food. Crucial to this efficiency are teeth: using teeth, animals can process food and turn it into smaller particles with larger surface areas, allowing easier access and energy extraction for enzymes in the animal’s stomach (Ungar 2015). Because of this high energy requirement and the relationship between teeth and proper mastication, tooth structure and shape is intimately connected with the tooth’s function and teeth are critical to the evolution of mammals (Ungar 2015). Teeth evolved to efficiently process a specific type of prey and therefore vary in form and function across taxa (Van Valkenburgh 1989; Meiri 2005; Friscia 2006; Popwics 2003). They most typically have complex crowns and are shaped in a way to efficiently process a specific type of food item (Van Valkenburgh 1989; Meiri 2005; Friscia 2006; Popwics 2003). The high degree of selective pressure exerted upon teeth is evidenced by the diversity of dental morphology across species (Valkenburgh 1989). For example, grazers (such as cows, Bos taurus) have large, high crowned teeth with enamel ridges that are able to grind up grasses and tolerate wear from grit consumed with food (Gailer 2016). In extant, small mammals, carnivores, insectivores, and omnivores can be identified using the length of carnassial blades and the size of molar grinding areas (Friscia 2006). Carnivores evolved a variety of different tooth forms to deal with differing dietary restrictions, including large blade- like carnassials in Felidae and Canidae for shearing and flat, square, four-cusped molars in Suidae and Ursidae for crushing. (Van Valkenburgh 1989). Because of their importance in processing food, a wide variety of studies look at variation in different aspects of tooth size and shape in species with relatively specialized, heterodont teeth (Meiri et al. 2005; Miller et al. 2009; Szuma 2000; Gingerich 1979; Dayan 2005; Baryshnikov 2003; Rozhnov 2006). Vulpes vulpes, the red fox, for example, has a high degree of variation in teeth that occlude less precisely between the top and bottom tooth (Gingerich,1979). The carnassial pair (the fourth premolar on the top jaw and the first molar on the bottom jaw) which occlude most precisely, have the least variation, followed by incisors with intermediate levels of occlusion (Gingerich 1979). The third molar, with the simplest occlusion, has the highest variation and is sometimes absent entirely (Gingerich 1979). We can see similar patterns of low variation correlated with degree of use in mastication and precision of occlusion with the bottom tooth in other terrestrial carnivores, including species in the families Felidae and Urisidae (Meiri et al. 2005; Miller et al. 2009; Szuma 2000; Gingerich 1979; Dayan 2005; Baryshnikov 2003; Rozhnov 2006). Coefficients of variation (CV) are a way to quantify variation while removing the effect of absolute size. Terrestrial mammals typically have relatively low CVs in teeth that occlude very precisely, such as carnassials, compared teeth that need not occlude precisely and have relatively low complexity, such as canines (Meiri 2005). CVs in certain species of canid and felid are consistently low. CVs of individual tooth lengths in Canis lupus vary from 3.68 to 8.83 with some of the lowest CVs found in measurements on the fourth premolar (the carnassial) (Dayan 2002). The first and second molar, two more teeth that precisely occlude with their corresponding lower tooth, also have some of the lowest CVs. Comparatively, the lengths of the pre-molars 2 P1, P2, and P3 have higher CVs (Dayan 2002). CVs for the wildcat species Felis silvestris, calculated in this same study are variable but often low. Like Canis lupus, the calculated CV for carnassial length (the fourth premolar on the upper jaw) in F. silvestris tend to be lower than some other premolars and molars, such as the second premolar and the first molar (Dayan 2002). F. silvestris also appears to follow the same pattern of high variation in less complex teeth that do not precisely occlude with bottom teeth and low variation in teeth that have complex shapes and crowns. Both of these species demonstrate relatively low CV scores (though some length measurements in F. silvestris can have high CVs, such as the length of the second premolar which has a CV of 25. 2). Ursids, members of the infraorder Arctoidea, also including Pinnipeds and Musteloids, tend to have intermediate levels of variation. Ursids, unlike either canids or felids, tend to be generalized omnivores with large, flattened, four-cusped molars with simplified crowns used for grinding (Miller 2009). The carnassial has been reduced and the other premolars are small and sometimes absent (Miller 2009). In the species Ursus americanus (the black bear), CVs ranged from 4.0 to 9.0, depending on the aspect and the sex of the animal and averaged 5.0 to 6.5 (Miller 2009). CVs for different tooth aspects in the cave bear Ursus spelaeus were similar to CVs for U. amercanus, with many CVs between 5.0 and 8.0 (though some aspects had CVs of around 11.0) (Baryshnikov 2003). In general, these terrestrial carnivores (U. americanus, U. spaleus, F. silvestris, and C. lupus) have similar levels of variation ranging from the 4.0 to 8.5 with some outliers, though measures in more precisely occluding, complexly crowned teeth are more variable in bears than other terrestrial carnivores (Miller 2009). 3 Musteloids, the other non-pinniped member of infraorder Arctoidea, also typically have low CV values.
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